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July 25, 2021 Archives

Sunday, July 25, 2021

TRACKING WITH CLOSEUPS: Contemporary Human Evolution Driven by Female Sexual Selection for Male Cognitive and Behavioural Traits

Here is the full paper, “Sex-biased reduction in reproductive success drives selective constraint on human genes” [PDF].

Summary:

Genome-wide sequencing of human populations has revealed substantial variation among genes in the intensity of purifying selection acting on damaging genetic variants. While genes under the strongest selective constraint are highly enriched for Mendelian disorders, most of these genes are not associated with disease and therefore the nature of the selection acting on them is not known. Here we show that genetic variants that damage these genes reduce reproductive success substantially in males but much less so in females. We present evidence that this reduction is mediated primarily by cognitive and behavioural traits, which renders male carriers of such variants less likely to find mating partners. These findings represent strong genetic evidence that sexual selection mediated through female mate choice is shaping the gene pool of contemporary human populations. Furthermore, these results suggest that sexual selection accounts for 21% of purifying selection against heterozygous variants that ablate protein-coding genes.

Posted at 13:46 Permalink

THE HAPPENING WORLD: The Case for Autonomous Vehicles

Note: this video was sponsored by Waymo, a subsidiary of Alphabet, Inc., the parent company of Google. Waymo is the spin-in company created to commercialise the technology developed by the Google self-driving car project. Waymo currently operates a driverless taxi service in Phoenix, Arizona, in the U.S., and is, at present, the only such service which operates without human back-up drivers.

This Veritasium video tries out the service, interviews some people from Waymo, and argues that even at the present “SAE Level 4” degree of autonomy, driverless vehicles are safer than the average human driver, so their introduction should be expected to reduce the number and consequences of motor vehicle accidents. This is the case made in the February 2021 Waymo Safety Report [PDF], which is referred to in the video.

This is far from a unanimous opinion, and presented by advocates engaged in developing and selling the technology. But here's their pitch.

Posted at 13:05 Permalink

CONTEXT: Double Jupiter Gravitational Assist

Posted at 12:47 Permalink

CONTINUITY: Restoring and Demonstrating an Early 1900s Nernst Lamp

The Nernst lamp was invented in 1897 by German physicist and chemist Walther Nernst (who would win the 1920 Nobel prize in chemistry for his work in thermochemistry). The Nernst lamp was an incandescent electric light which used a ceramic rod composed of oxides of yttrium and zirconium instead of the carbon filament employed by the contemporary Edison light bulb. The Nernst lamp produced about twice the light for a given amount of electricity as carbon filament bulbs, and emitted a whiter, more sunlight-like spectrum. Because the light-emitting element was already completely oxidised, it did not require a vacuum or inert gas environment, and operated with no problem in air (although lamps were usually enclosed in a glass bulb to protect objects from touching the hot element).

The main disadvantage was that the ceramic used did not conduct electricity at room temperature, and needed to be initially warmed to its conduction temperature by a separate heater, after which it would self-heat through electrical resistance. Consequently, Nernst lamps required a “starter” circuit not unlike that of fluorescent lights to initially engage the heater and then disconnect it after the light came on.

Due to its efficiency and more natural light, the Nernst lamp became popular, initially in Europe where it was manufactured by AEG in Germany. In the U.S. George Westinghouse licensed the design in 1901 and manufactured it domestically as it evaded Thomas Edison's patents on his light bulb, selling more than 130,000 by the year 1904.

Subsequently, development of tungsten filament bulbs, which emerged in their modern form during the 1910s and were more efficient and less complicated and expensive than the Nernst lamp, rendered it obsolete. Today Nernst lamps are scarce and expensive collectors' items and even more rare to see in working condition.

Posted at 11:49 Permalink